1. Field of the Invention
The invention relates to a method of stabilising the bonding agent gelation time in the consolidation of a geological formation in the presence of catalytically active substances, the use of a bonding agent therefor and the bonding agent used therefor.
2. Discussion of Background Information
Bonding agents for bonding embankments and loose formations are known. Thus e.g. DE-A-102004004615, EP-A-06706316, WO 2007/121972, WO 2007/121975 and WO 2009/106562 describe systems which are used for the consolidation of embankments or loose formations. The procedure is generally such that a reactive soluble system infiltrates into an embankment or loose formation and is solidified by way of a reaction. If the curing is effected by means of a radical polymerization process, peroxides are commonly used as thermal polymerization initiators.
Peroxides of widely varying type are known as important radical starters in the polymerization of organic double bonds, particularly in olefins. The mechanism is based on the dissolution of the oxygen-oxygen bond into two fragments containing radicals, which transmit their radical electron to the double bond and thus stimulate a chain reaction, which finally results in the formation of polymers. The dissolution of the oxygen-oxygen bond can be effected by the supply of energy, for instance thermal or light energy.
The stability of the oxygen-oxygen bond depends very strongly on the structure of the molecule which carries this bond. Depending on the compensation ability of the polarity of the oxygen-oxygen bond by the remaining bonds in the molecule, the formation of radicals is possible by the dissolution of the oxygen-oxygen bond in relatively diverse temperature ranges. This has been made use of to control the polymerization temperature of olefins in chemical engineering. Working temperatures of 20-120° C. for initiating the polymerization are possible.
Due to the metastability of the oxygen-oxygen bond, catalytically active compounds can significantly alter the thermally determined decomposition temperature and thus the formation of radicals. Thus it is, for example, known that metal ions, such as copper ions or iron ions, have a significant influence on the decomposition temperature. Furthermore, crystalline compounds, such as oxides, e.g. aluminium oxides, silicate deposits or iron oxides, can influence the decomposition temperature. Understandably, the smaller the oxide structures the greater is this effect. This is known from catalyst chemistry, for which reason there is a tendency to use catalytically active solid bodies in as small a division as possible (enlargement of the active surface; nanocatalysis).
However, components which act catalytically on the decomposition temperature are disruptive in many applications, particularly if it is not known what components are present in what concentration in certain usages. Control of the polymerization process is then difficult if not impossible. Furthermore, other thermodynamic parameters, such as the pH value, or the solvent, can have a strong influence on the decomposition rate and radical formation.
A precise adjustment of the parameters is, however, extremely difficult, if not impossible, in the intended application, namely when treating a geological formation in the extraction of oil and gas.
Thus the bonding agent can be contaminated with metal ions and iron oxides even when being pumped into the formation by contact with conduits and production equipment. The pipes are generally of soft steel and thus not very corrosion-resistant because they must be coiled up and used in so-called coils of up to many 1000 m of length. These coils are generally coated internally by a rough layer of rust and it has transpired that both these layers of rust and also the bare metal have a very strong catalytic effect on the decomposition of peroxides, whereby the gelation time can shorten considerably when using peroxides as initiators.
A further critical point is the extremely variable composition of the geological formations, e.g. as regards the minerals which are present, sand types, porosity etc. This means that such binders based on peroxide initiators can be critical or too unstable, depending on the geographical location.
One application, in which these effects are particularly disruptive is, as already briefly noted, the application of bonding agents with monomers, which are to be solidified, in the oil and gas producing industry. For example, in order to stabilize geological formations, monomers with polymerizable double bonds in dissolved or liquid form are pumped into them. The higher temperatures, which generally prevail in the formations, are used for the radical polymerization. It is of importance that this occurs only in situ as a result of the temperature-determined decomposition of the initiators and not previously as a result of catalysis since there is otherwise the risk of the blockage of feed lines, pumps and valves and also of the pores in the formation. The setting characteristics of the bonding agents must thus be so set that solidification reliably begins only when the infiltration and the recreation of the permeability of the formation has come to an end.
In tests to determine the polymerization time with so-called inorganic-organic bonding agents, e.g. Nanoglue®, with which the solidification proceeds as a result of silanes with methacrylate groups and as a result of diacrylates by polymerization in the formation, it has been ascertained that components of the formation, metals or iron oxide-containing components, e.g. in the form of sands, influence the formation of radicals with peroxides in an uncontrollable manner and forecasts are scarcely possible with regard to the desired temperature-determined polymerization after injection of the bonding agent into the formation.
Thus, for example, on contact with the coiled tubing or the addition of sands of differing grain size, grain shape and minerality when using peroxides, differences in the gel formation time of over 50% have been observed. It is problematic in this connection that an uncontrolled acceleration could be observed in each case, whereby the risk of premature setting of the bonding agent is considerably increased.
Using such systems, which essentially have an excellent solidification mechanism, in the oil and gas industry is thus risky if not wholly impossible.
The object was the provision of a robust bonding agent and a method of consolidating geological formations with this bonding agent, in which the gelation time of the bonding agent is not altered uncontrollably, in particular is not shortened, by the nature and concentration of additional additives in the bonding agent, changes in pH and, in particular, the conditions in the geological formation, such as nature and concentration of the minerals and the catalytically active substances etc.
It has now surprisingly been found that other radical formers, which include no peroxide functionality, such as azo compounds or compounds with a C—C single bond, which can be homolytically dissociated by thermal energy, do not exhibit a shortening in the gelation time or only to a very small degree. It has transpired that when using such radical starters in the polymerization of the inorganic-organic bonding agent in the formation, the iron content plays no role or only a very small role, i.e. the gelation time is scarcely influenced or slightly extended, whereby the pumping in and the flushing of the bonding agent can be ensured. The use of radical starters without peroxide functionality results in an adequate constancy of the gelation times on contact with different substances. This system does not react with a shortening of the gelation times on the addition of metal ions, special sands or on contact with coiled tubing, as was observed with peroxides.
This was not to be anticipated. Without wishing to be bound by a theory, this phenomenon can perhaps be explained by the fact that the ionic or catalytically active systems referred to above, as are common in the crude oil industry in the production equipment and formations, act on peroxides via unknown mechanisms whilst azo compounds, on the other hand, are more or less uninfluenced. On the basis of this surprising fact, a binder system, such as the described Nanoglue® system, can be used with azo compounds or other non-peroxide initiators for the intended application for stabilizing oil and gas sources.